I think that Mindovermaster is mostly correct. If one of the drives fails, you will need to get another drive to rebuild the array. If the motherboard fails, you can move both drives to another machine and still access them as a RAID array; MDADM writes headers to both drives indicating they are part of the RAID group so motherboard failure shouldn't affect that. You can find a good RAID 1 tutorial (for Debian Etch, but it should work just as well for Ubuntu 12.04) here.

Yeah, motherboards don't really fail very often. The great thing about RAID 1 in Linux is its resiliency. Since it doesn't rely on any special hardware or a software configuration that can't be easily replicated, its very easy to recovery in almost any situation. Take it from experience: RAID 1 is indispensable when you have major hardware failure with critical business data.